Try the; "Scroll Lock" button on the PC keyboard.
This will open up the ATC Window.
You can also assign it to a button on your Joystick.
Sometimes, with problems, its worth re-starting the Sim again from scratch!
Paul....

...!
Win 8.1 64-bit. DX11. Advent Tower. Intel i7-3770 3.9 GHz 8-core. 8 GB System RAM. AMD Radeon HD 7700 1GB RAM. DVD ROM. 2 Terra Byte SATA Hard Drive. Philips 17" LCD Monitor. Saitek Cyborg X Fly-5 Joystick. ...and a Briggs and Stratton Petrol Lawn Mower.